Radar is a device or system consisting of an emitter that emits waves (RF, acoustic, etc.) that reflect off objects and a receiver that receives the reflections of the emitted waves for processing to detect, track or locate the objects. Various radar systems are known for detecting presence of objects, persons, things, etc. In one application, a security radar system detects unauthorized intrusions into a protected area. Such security systems operate based on activation of an intrusion sensing device, such as an acoustic motion detector, to generate an alert or alarm when an unauthorized intrusion is detected, for example, by placing a call to a remote police station. Systems that detect presence of objects have also been used to provide information related to the number and position of objects, things or persons within enclosed structures. Such systems have also been used to find survivors within the rubble of collapsed buildings.
The so-called “first time responders,” such as law enforcement officers and fire fighters, etc., have also used such detection systems for surveillance and for providing situational awareness for risk reduction or decreasing unknowns. The acoustic solution for detecting presence of an object, for example, uses a very sensitive listening device (i.e. microphone), or array of them, to process incoming noise. The disadvantage of acoustical systems lies in the fact that without an array of directional listening devices, it is almost impossible to determine the location of the targets that generate noise. Furthermore, moving targets may not make enough noise to be detected. On the other hand, the optical solution has been used to view the interior of the structure through a window, or to find a crack in the structure through which to view the interior, or actually drill a hole so that a camera could be inserted for surveillance. The drawbacks of this solution are that it takes time to find a crack or drill a hole and it is noisy to do so. Thus, in a hostage or raid situation, the law enforcement personnel could lose the tactical advantage of surprise. Additionally, the view through a window or crack may only provide a limited field of view, and so, parts of the room may be hidden. Moreover, if the room is smoke filled then this solution is ineffective. Finally, the IR solution is an optical solution that cannot be implemented without a direct view.
Radar systems are also known for detecting presence of objects. Serious developmental work on radar began in the 1930s, but the basic idea of radar had its origins in the classical experiments on electromagnetic emission conducted by the German physicist Heinrich Hertz during the late 1880s. As is well known, radars emit electromagnetic waves (also known as radar radio signals) and detect presence of an object by processing reflections off the object at a receiver. Known radar radio signals cover a wide frequency spectrum, ranging from narrow band to ultra-wideband (UWB) radar signals. UWB radar signals exhibit many desirable features that would be advantageous in various environments. These features include high range resolution, low processing sidelobes, excellent clutter rejection capability, and the ability to scan distinct range windows. Additionally, the technique of time modulated UWB (TM-UWB) adds decreased range ambiguities and increased resistance to spoofing or interference. UWB radar can operate on wavelengths capable of penetrating typical non-metallic construction material. These advantages make UWB radar particularly beneficial in short range, high clutter environments.
Various types of UWB radars are known. For example, a mono-static radar transmits radar signals from one location and receives reflections at the same location, whereas a bi-static radar transmits radar signals at one location and receives the reflections at another location. One such radar system is known as RadarVision®, which is developed and manufactured by Time Domain Corporation, the assignee of the present invention. First time responders, SWAT team members, and others use the RadarVision® to “see through walls” to determine the number and position of moving objects, persons, or things on the other side of the wall to support tactical decision-making.
UWB radars have beneficial applicability in environments where vision is obscured by obstacles such as walls, rubble, or smoke, and fire. Various embodiments of UWB radar have been described in co-owned U.S. Pat. No. 4,743,906, issued to Fullerton, May 10, 1988; U.S. Pat. No. 4,813,057, issued to Fullerton, Mar. 14, 1989; and U.S. Pat. No. 5,363,108, issued to Fullerton, Nov. 8, 1994, all of which are incorporated herein by reference. Moreover, arrays of such radars have been developed for such uses as high resolution detection and intruder alert systems, as described in co-owned U.S. Pat. No. 6,218,979 B1, issued to Barnes, et al. Apr. 17, 2001; and U.S. Pat. No. 6,177,903, issued to Fullerton, et al Jan. 23, 2001, respectively, both of which are incorporated herein by reference. An alternative ‘scanning receiver’ approach to UWB radar is described in U.S. Pat. No. 6,614,384, issued to Hall, et al. Sep. 2, 2003, which is also incorporated herein by reference. These systems benefit from being low power and non-interfering, and yet are capable of scanning through typical, non-metallic building material.
With the increased need for sophisticated surveillance in view of security threats facing the world as well as the increased need for meeting challenges associated with public safety, emergency and disaster situations, there still remains an ongoing need for simple and effective systems and methods for detecting the presence of objects, things or persons under a wide variety of circumstances.